JP2007060354A - Image processing method and device, image reading device, image forming device, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct uneven coloring with high accuracy in a simple constitution if it is caused by a variation in optical component member characteristics, in an image reading device equipped with an uneven coloring correction function. <P>SOLUTION: For each color data of R, G, B of an processing object, gain correction for each reading position is applied to processing objective data of color (R, G, B) and at least one color data (G to R or B, and R or B to G) other than R, G, B so that color data can be obtained with corrected uneven coloring. At this time, subtraction data Δ between two colors is generated by a subtraction unit 412. In a correction arithmetic processing unit 414, the data are multiplied by a correction coefficient α read from a correction coefficient storing unit 415, where a correction coefficient for each subtraction data Δ is stored previously, and added to the original color data DR1, DG1, DB1 so that corrected data DRc, DGc, DBc can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing method, an image processing apparatus, an image reading apparatus, an image forming apparatus, and a program. More specifically, the present invention relates to a mechanism for correcting color unevenness caused by variation in characteristics of optical members such as a sensor of an image reading unit and an infrared cut filter.

  In a conventional image reading apparatus using an image sensor, it is caused by a difference in element sensitivity of the image sensor or a difference in characteristics of an optical system that forms an image of an original image on the image sensor without distinguishing between black and white and color. Even if a document image having a uniform density is read, the output of each element of the image sensor is not uniform and uneven. Generally, shading correction is performed to eliminate this problem.

  In this shading correction, white shading correction is generally performed. For example, a correction gain is calculated for each pixel based on data read by illuminating a reference white plate with an illumination light source and a preset reference value, and stored in the memory. The gain is read out and multiplied by the correction gain for each pixel to suppress uneven density in the image data.

  However, with the conventional white shading correction alone, sufficient correction is difficult except for a low-saturation white document area, and as a result, when a highly saturated color is read, the main scanning direction is displayed on the output image. Color unevenness exists in the.

  For example, in the case of an image reading unit that performs full-color reading, a sensor device is usually provided for each primary color of R, G, and B, and these sensor devices are generally each photodetector of a photodetector array manufactured by a semiconductor process. It is created by covering (pixel) with a color filter of a corresponding color.

  For example, a color image scanner in which an RGB color stripe filter is printed on a pixel-by-pixel basis performs color separation based on read data of three consecutive pixels and handles it as image data for one pixel. As a result, part of two adjacent filters overlap each other, or the entire surface of the element is not covered by the filter, so that the spectral characteristics differ from element to element, and a low-saturation document area can be obtained only by white shading correction. Except for this, sufficient correction is difficult. That is, with the conventional mechanism, correction of the chromatic original region is insufficient, and unevenness in element spectral sensitivity cannot be removed, resulting in uneven color in the main scanning direction. Will appear.

  Further, when a line sensor is used as the image reading unit, if the A4 size horizontal width is covered, a line sensor having that width is provided for each of R, G, and B colors. In this case, in order to obtain a reading resolution of several hundreds dpi (dots / inch), each line sensor has a photo detector for several thousand pixels arranged in a line. It is difficult to form a color filter so as to have a uniform thickness over the entire area of such a long width, and in reality, the thickness gradually increases from one end of the line sensor to the other end. Thus, unevenness in filter thickness (irregularity in filter density) can be produced. In an application in which in-plane unevenness of print output, which will be described later, is detected by image reading, the in-plane unevenness of printing is very small. Therefore, the difference in sensitivity between the photodetectors due to uneven filter density has a great effect on in-plane unevenness measurement.

  Even for in-plane unevenness of printing, neutral density (grayscale) unevenness is not affected by the spectral characteristics of the filter, so it can be corrected to some extent by collecting and correcting white and black standards within the page surface. . However, the color component unevenness is directly affected by the difference in the spectral characteristics of the filters of each photodetector due to the filter density unevenness. Therefore, the detection signal of each photodetector has uneven filter density in the printing surface. The effect is superimposed. For this reason, in order to correct the in-plane unevenness, it is necessary to remove the error component due to the filter density unevenness included in the detection signal of the photodetector, so that the correction is not easy.

  In addition to the problem of uneven density of the on-chip filter, interference filters such as a color filter and an infrared cut filter constituting a dichroic prism also have a spectral angle of view characteristic. There may be a difference in sensitivity and similar problems may occur.

  For this reason, various mechanisms for correcting not only white shading correction but also color unevenness have been considered (see, for example, Patent Documents 1 to 4).

JP 2003-072206 A Japanese Unexamined Patent Publication No. 62-293877 Japanese Patent Laid-Open No. 06-152954 JP 2002-171417 A

  For example, as a function of an image reading unit of a digital copying machine, there are applications of calibrating output characteristics between color printers and detecting in-plane unevenness of a color printer in addition to a reading device for a copying machine and a scan-in terminal. As an example, the mechanism described in Patent Document 1 is a method of monitoring the state of the printing unit by reading the print output of the printing unit with an image reading unit.

  In the mechanism described in Patent Document 1, an inspection chart is printed for shading correction of a print head of an ink jet printer or an LED printer, and the print result is read by an attached image reading unit, whereby ink of an ink jet nozzle is printed. Density unevenness caused by variations in the discharge amount and the emission intensity of the LED is detected and corrected.

  On the other hand, in an electrophotographic laser color printer, the development gap, transfer performance, and the like may slightly change along the main scanning direction, that is, the axial direction of the photosensitive drum. In addition, minute print density unevenness (in-plane unevenness) may appear. When high-quality printing equivalent to offset printing is to be realized, it is necessary to accurately detect and correct such uneven printing density in the main scanning direction.

  For this purpose, for example, an inspection chart having a uniform color and density in the main scanning direction is printed on the printing unit, and the printing result is read to measure the distribution of the printing density along the main scanning direction. Preparing a dedicated measuring device for this measurement is a place you would like to avoid if you can see it in terms of cost. As described above, the inspection chart printed on the printing unit of the multifunction device is read with the attached reading unit to check for unevenness. If possible, it is preferable not only in terms of cost but also in terms of work efficiency.

  However, in such calibration of output characteristics and in-plane unevenness detection, the in-plane spectral characteristic variation as described above becomes a problem. For example, a color difference of about “1” in the CIELAB color system is required as in-plane reading unevenness, but the requirement has not been satisfied at present.

  Further, in Patent Document 2, in a reading apparatus using a multi-chip type sensor that connects a plurality of line sensor chips to cover a long main scanning section, a correction circuit is provided at the output of each chip, and the correction circuit is variable. A mechanism is disclosed that corrects in an analog manner so that the output of each chip becomes uniform by appropriately adjusting the resistance. Although this mechanism is an old technology, if the same idea is promoted, it is conceivable that correction data corresponding to the filter density is obtained for each pixel of the line sensor and the detection signal of each pixel is corrected with the correction data. .

  However, even if filter density correction data is prepared for each pixel of the line sensor in this way, it is not possible to remove the influence of the filter density with sufficient accuracy to the extent necessary for the purpose of detecting minute in-plane unevenness. Can not. This is because, as described above, the transparency of the base portion of the spectral response of the filter varies greatly due to the difference in filter density, and the degree of this variation also varies depending on the type of color material and the printing density.

  In addition to the color unevenness correction described above, correction of color characteristics caused by the reading system device includes correction to convert to standard color coordinates. If both are performed at once, the latter conversion is strong. Since it has non-linear conversion characteristics, it is assumed that new unevenness occurs in pixel units and small block units due to the difference in conversion characteristics, and enormous man-hours and memory capacity are required. In addition, there is a concern that accuracy may decrease due to fluctuations during the collection of several tens of pieces of correction output data.

  Patent Document 3 proposes a mechanism for correcting color unevenness due to spectral characteristic unevenness in the main scanning direction. In the mechanism described in Patent Document 3, the color shading of an image subjected to white shading is measured by examining the spectral distribution, and white shading is performed so that unevenness in color tone is reduced based on the measurement result. For each of the R, G, and B color data subjected to the above, correction is made for each element constituting the sensor while referring to the pixel address.

  However, with this mechanism, R (G, B) data with corrected color unevenness is obtained by performing gain correction with reference to color tone on any one of R, G, and B data subjected to white shading correction. Therefore, it is impossible to perform color unevenness correction in consideration of both hue and saturation. With only the color tone information, it is not possible to take into account the difference between a brightly saturated color and a color close to an achromatic color, and correction cannot be made with an appropriate amount corresponding to the difference in saturation.

  Further, in Patent Document 4, a color patch is provided in an image reading unit, and a color patch read value by a scanner CCD of the image reading unit and a color patch read value by a scanner CCD having a standard spectral light property are used. A mechanism for correcting the read value of the gradation pattern by obtaining the ratio has been proposed.

  However, the mechanism described in Patent Document 4 corrects variation in CCD spectral characteristics, and manually or automatically corrects changes in CCD spectral characteristics over time and color patch changes over time. The correction is made so that the YMCK density set later does not vary from machine to machine and a good gray balance can be obtained. In short, it is only intended for machine differences. Therefore, in-plane read color unevenness cannot be corrected simply by using the mechanism described in Patent Document 4.

  The present invention has been made in view of the above circumstances, and can correct color unevenness that may occur due to variations in the characteristics of the optical member of the image reading unit with higher accuracy while being a simple mechanism. The purpose is to provide a mechanism.

  In the mechanism according to the present invention, in correcting the color unevenness existing in the read image, for each color data to be processed, for example, for each color data of R, G, B, the color to be processed (R, G in the previous example) , B) and at least one other color data (G for R and B, R and B for G) are corrected by applying gain correction for each reading position. Acquired finished color data.

  The inventions described in the dependent claims define further advantageous specific examples of the mechanism according to the present invention. Furthermore, the program according to the present invention is suitable for realizing the color unevenness correction mechanism according to the present invention by software using an electronic computer (computer). Note that the program may be provided by being stored in a computer-readable storage medium, or may be provided by distribution via wired or wireless communication means.

  For example, if color data that has been corrected for color unevenness is acquired based on the result of gain correction performed on the function of the difference between the two color data, the color can be displayed with little effect on the achromatic color data. Unevenness correction can be realized.

  Furthermore, if color data that has been corrected for color unevenness is acquired based on the result of gain correction applied to the power of the difference function between the two colors of data, it will have little effect on the achromatic color data. In addition, color unevenness correction can be realized while further improving accuracy.

  Further, when color unevenness correction is performed, color data in a predetermined color space representing a read image is converted into standard color coordinate data and output (typically output to an image forming unit). As a matter of course, before conversion to standard color coordinate data, it is possible even after conversion to standard color coordinate data.

  In addition, a standard coefficient is set in the conversion function to the standard color coordinate data, and the color data that has been corrected for color unevenness is converted into standard color coordinate data in the function for correcting color unevenness. Also good.

  According to the mechanism of the present invention, color unevenness is obtained by applying correction using information of a target single color and at least one other color for each color data to be corrected such as R, G, and B color data. Since corrected color data is acquired, high-accuracy color unevenness correction considering both hue and saturation can be realized, and in-plane color unevenness correction in the main scanning direction and other color corrections can be realized. Relevant functions (for example, correction conversion to standard color coordinate data) can be achieved with a relatively simple configuration.

  This makes it possible to correct unevenness in the reading surface due to, for example, on-chip filter unevenness of the sensor and spectral field angle characteristics of the optical system, and to provide color reading characteristics with accuracy that can be used for in-plane unevenness measurement of print output. Can be realized. In addition, the amount of correction data necessary for the in-plane color unevenness correction function can be realized on a realistic scale.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Outline of device appearance>
FIG. 1 is a side sectional view showing an outline of an embodiment of an image reading apparatus including an image processing apparatus including an example of an in-plane position reference type color unevenness correction unit according to the present invention. An image reading apparatus 3 shown in FIG. 1A is used for, for example, a copying machine, a scanner apparatus, and a facsimile apparatus, and optically reads an image drawn on a document to be read. In general, the image acquisition unit 10, the image processing unit 40, and the platen cover 61 are provided. When configuring an image forming apparatus such as a copying apparatus or a multifunction peripheral, the image reading apparatus 3 and an image output unit (print engine) are combined (see FIGS. 3 and 16 described later).

  The image acquisition unit 10 includes a casing 111 and a platen glass (original placement table) 112 that is made of transparent glass provided on the casing 111 and is slightly larger than the A3 size on which an original to be read is placed. have. The image processing unit 40 is provided on the image processing substrate 102 provided in the housing 111.

  In the case of constituting a copying apparatus, the image signal processed by the image processing unit 40 generates a visible image on a predetermined recording medium using a known printing method such as a thermal sublimation method, an ink jet method, or an electrophotographic method. The image data is sent to an image output unit including a printer engine (image forming unit) to be formed.

  The image acquisition unit 10 irradiates reading light toward the surface (back surface) opposite to the document placement surface of the platen glass 112 below the platen glass 112 in the casing 111, that is, the document on the platen glass 112. An exposure light source 120 that irradiates reading light toward the platen, and a substantially concave reflecting shade 131 that reflects the reading light emitted from the exposure light source 120 toward the platen glass 112.

  The image acquisition unit 10 receives reflected light from the platen glass 112 side and performs a main scanning FS (Fast Scan) that is substantially orthogonal to the direction of the sub-scanning SS (Slow Scan) (the reading direction of the arrow X in the figure). A light receiving unit 140 that sequentially reads an image signal (analog electric signal) corresponding to the density, reads the image in the direction (the depth direction in the drawing), and amplifies and outputs the image signal from the light receiving unit 140 to a predetermined level. The contact optical system includes a read signal processing unit 14.

  The light receiving unit 140 includes a photoelectric conversion element such as a photodiode, a CCD (Charge Coupled Device), a CMOS (Complementary Metal-oxide Semiconductor), and the like, and is a line having a width (also referred to as a full width) substantially equal to the width in the main scanning direction of the document. Use a sensor.

  In the case of color imaging, in order to increase the resolution in the main scanning direction, for example, a 7500 pixel full width line sensor is prepared for each color of R, G, and B, and is provided at a predetermined interval L1 (reading) in the sub scanning direction. A so-called three-line color sensor system is employed in which the pixel columns are also arranged at intervals.

  Each line sensor for each color is provided with a color filter for that color on-chip. A so-called on-chip filter configuration is employed. In addition to the color filter, an optical member such as a microlens that increases the light collection efficiency may be provided.

  Alternatively, instead of the three-line color sensor method, an in-line sensor method in which R, G, and B color filters (and also microlenses, etc.) are repeatedly arranged in the main scanning direction may be employed.

  In the in-line sensor method, the resolution in the main scanning direction is lowered, but there are few problems of three-color registration errors when the original is read while being conveyed. On the other hand, in the case of the three-line color sensor system, improvement of this three-color registration error is required. For example, a CCD register must be provided between the pixel columns, and it is necessary to ensure a certain interval between the pixel columns. On the signal processing side, a line memory is required to compensate for the deviation of the reading position. In order to reduce the line memory, it is preferable to reduce the interval between the read pixel columns of the three line sensors as much as possible (see paragraph 0009 of Japanese Patent Laid-Open No. 8-172178 and paragraph 0005 of Japanese Patent Laid-Open No. 2000-223690).

  However, if such a measure is taken, it becomes difficult to accurately form an on-chip filter, a microlens, or the like in each read pixel row, and thus the spectral characteristic variation performance is hindered.

  Note that the line sensor has a structure having a plurality of pixels in the main scanning direction, and there is unevenness in the main scanning direction in reading spectral characteristics due to variations in the thickness of an on-chip filter provided on the pixels and an optical system. As a result, brightness unevenness and color unevenness may occur in the main scanning direction.

  As is well known, brightness unevenness is improved by so-called shading correction in which correction is performed by standardizing data for each color using, for example, a standard output of white reference data.

  On the other hand, with regard to color unevenness, it is not sufficient to perform only the shading correction for the above-described lightness unevenness, and when dealing with only shading correction, color unevenness in the main scanning direction is output on the output image when a highly saturated color is read. It will exist. As this countermeasure, the details will be described later, but this is dealt with by correcting the uneven color of the in-plane position reference type by the second color correction unit.

  In addition, as a full width line sensor, m sensors having a width of 1 / m with respect to the width in the main scanning direction are usually arranged in series. However, in this case, a mechanism for absorbing the spectral characteristic difference for each line sensor in the main scanning direction is required, and in the standardized color correction unit that performs conversion to a standard output using a color correction matrix calculation described later, In order to change the color correction coefficient corresponding to the line sensor, a standardized color correction unit is provided corresponding to each line sensor.

  The light receiving unit 140 is disposed on the reading substrate 103 together with the reading signal processing unit 14 and the like, and constitutes an optical scanning system (sensor unit) 16. As shown in FIG. 1B, a reading optical system employing a reduction optical system such as an exposure light source 120, a full rate carriage 134, a half rate carriage 138, or a lens 139, instead of the light receiving mechanism using the contact optical system. A mechanism of (scanning optical system) may be adopted.

  As the exposure light source 120, a lamp whose longitudinal direction is the main scanning direction is used. The lighting operation of the exposure light source 120 can be controlled by an illumination control unit (not shown).

  In the drawing, a white reference plate 116 used for white shading correction is included on the left side of the platen glass 112 in order to perform shading correction. Note that not only the white reference plate 116 but also a black reference plate for black shading correction may be included. As the white reference plate 116, for example, a plate made of a material having a light reflectance close to “1” is used. The black reference plate is made of a material having a light reflectance close to “0”.

  Although not shown, the image acquisition unit 10 also includes a wire, a drive pulley, and the like for moving the reading optical system, the light receiving unit 140, and the like under the platen glass 112 in the housing 111. The driving pulley is reciprocally rotated by the driving force of the driving motor, and the optical scanning of the exposure light source 120 or the lens 139 is performed below the platen glass 112 by winding the wire around the driving pulley by this rotational driving. The system 16 is moved at a predetermined speed.

  In this fixed reading method, a document is placed on a platen glass 112 serving as a document placement table, and is fixed (stop-locked) at an arbitrary position on the platen glass 112. Using the fixed reading image destination position F as a reading reference, the optical scanning system 16 is scanned at a constant speed in the direction of the arrow X (sub-scanning direction) to expose a document and read an image.

  The light receiving unit 140 sends captured image signals of each spectral component obtained by capturing a document image with a line sensor to the read signal processing unit 14. The read signal processing unit 14 performs desired analog signal processing on the captured image signal obtained by this reading, and then converts the digital image data of each color component of red (R), green (G), and blue (B). After the conversion and shading correction and other predetermined processing, red, green and blue digital image data are sent to the image processing unit 40.

In the image processing unit 40, for example, processing for synchronizing digital image data R, G, and B of color components output from the read signal processing unit 14, brightness signal L and color signals a and b (collectively Lab; Performs color conversion processing for generating L ^* a ^* B ^* ).

  In the image reading apparatus 3 shown in FIG. 1A, a normal platen cover 61 is used. However, as shown in FIG. 1B, an ADF (Automatic Document) having a function of the platen cover 61 is used. A Feeder (automatic document feeder) device can also be used. Further, an automatic document feeder (DADF) having a circulation function can be used.

  Although the image reading apparatus 3 is shown as a single unit, the image reading apparatus 3 can be used as a scanner unit to constitute a copying apparatus. In this case, for example, an image output unit is provided below the image acquisition unit 10, and black (K), yellow (Y) based on the red, green, and blue image data R, G, and B from the image processing unit 40. , Magenta (M), cyan (C) binary or multivalued output image signal output image processing unit, and a recording medium such as printing paper based on the output image signal obtained by the output image processing unit An image forming unit (printer engine) for forming a visible image may be provided on the top.

<Configuration example of light receiving unit>
FIG. 2 is a diagram illustrating a configuration example of the light receiving unit 140. Each of the first example shown in FIG. 2A, the second example shown in FIG. 2B, and the third example shown in FIG. 2C is of a three-line color sensor type using a CCD. .

  As shown in the figure, the light receiving unit 140 has three line sensors 142R corresponding to the three colors R, G, and B so that the components of the three colors R, G, and B can be detected for color image capturing. , 142G, 142B (collectively referred to as 142; the reference indicates the color). These line sensors 142R, 142G, 142B are arranged so as to be read in the order of R, G, B in the sub-scanning direction.

  Each line sensor 142 is configured by arranging a large number of photoelectric conversion elements (photodiodes) having a predetermined pixel size, for example, a pixel size of 7 μm × 7 μm, in an array corresponding to one line in the main scanning direction.

  That is, in the package of the light receiving unit 140, line sensors 142 in which n photoelectric conversion elements having a pixel size of 7 μm × 7 μm are arranged are arranged in three rows at predetermined intervals. Each of these line sensors 142 is means for reading a document image at each reading position in the sub-scanning direction. Each photosensitive unit includes a photoelectric conversion element such as a photodiode that photoelectrically converts incident light, and a charge storage unit that accumulates charges generated by the photoelectric conversion element. In the figure, 1, 2, 3,... Attached to the line sensor 142 indicate pixel numbers.

  Here, the first example shown in FIG. 2A uses the line sensor 142 of FIG. 1B, and the line sensors 142R, 142G, 142B are separated by L1. Correspondingly, in the case of the reduction optical system, the reading positions of the respective color components in the sub-scanning direction on the document transport path are separated by L2. Each original image (line image for one line) at each reading position is reduced to L1 / L2 times through the reading optical system shown in FIG. 1 and is connected to each line sensor 142R, 142G, 142B. Image. That is, the distance L1 between the three line sensors 142 corresponds to the distance L2 at the document position before being condensed by the lens 139, and the three line sensors 142 simultaneously read the positions separated by L2 of the document G. For this reason, this misalignment is corrected by a synchronization process (described later) in which the positional deviation is replaced with a time deviation on the premise that the original and the sensor are moved at a relatively interrogating speed, but is read while the original is being conveyed. At this time, a three-color registration error due to a change in the conveyance speed can be a problem.

  On the light receiving surfaces of the three line sensors 142R, 142G, and 142B, color filters corresponding to the R, G, and B color components are separately provided. Thereby, these line sensors 142R, 142G, and 142B function as means for reading an optical image for each of the RGB color components for capturing a color image.

  For example, when arranged so as to be read in the order of R, G, and B in the sub-scanning direction, the R line sensor 142R has n photons constituting the line sensor 142R every one line period (main scanning period). The charges accumulated in the diode are transferred to the transfer register by the vertical transfer pulse, the charges in the transfer register are sequentially transferred horizontally by the horizontal transfer clock, and the charge voltage is converted by the final stage amplifier for one line (for n pixels). Are output as an analog imaging signal SR representing the density of each pixel.

  Similarly, the G line sensor 142G corresponding to the reading position on the downstream side of the line sensor 142R also corresponds to the signal charge detected by the n photodiodes for each line period (main scanning period). Thus, an analog imaging signal SG representing the density of each pixel for one line (for n pixels) is output. Further, in the B line sensor 142B corresponding to the reading position downstream of the line sensor 142G, the signal charges detected by the n photodiodes are corresponding to each line period (main scanning period). An analog imaging signal SB representing the density of each pixel for one line (for n pixels) is output.

  Here, the interval L1 of each line sensor 142 corresponding to each reading position (interval L2) of each color component is an interval corresponding to scanning lines for L1 / 7 (“7” is the pixel size) lines. For example, if the interval L2 between the reading positions of each color component is 169.2 μm and the interval L1 between the line sensors 142 is 28 μm, the number of lines is four. Therefore, if there is no change in the document conveyance speed, the R component imaging signal SR and the G component imaging signal SG, or the G component imaging signal SG and the B component imaging signal SB are L1 / 7 (4 in the previous example). Line) The signal has a considerable phase difference. Note that the distance L1 between the line sensors 142R, 142G, and 142B for color image capturing is not limited to the above-described example, and may be appropriately determined in consideration of the entire configuration of the image reading apparatus.

  The second example shown in FIG. 2B uses the line sensor 142 of FIG. 1B as in the first example, but the capacity of the line memory used to improve the three-color registration error. In order to reduce this, the interval L1 between the read pixel columns of the 3-line sensor is reduced. In this configuration example, L1 is made equal to one line, that is, the pixel pitch in order to facilitate the gap correction calculation.

  The third example shown in FIG. 2C is a modification in which m line sensors having a width of 1 / m with respect to the width in the main scanning direction are arranged in series as the full width line sensor. Here, as indicated by 142_1, 142_2, 142_3, 142_4, four line sensors 142R, 142G, 142B are arranged in series with four quarter widths in the main scanning direction. In addition, it can replace with the full width line sensor of the 1st example shown to FIG. 2 (A), and can change similarly.

<Signal Processing System of Image Acquisition Unit; First Embodiment>
FIG. 3 is a block diagram illustrating the first embodiment in detail focusing on the signal processing function of the image acquisition unit 10.

  The image acquisition unit 10 includes a central processing control unit 180 that controls the image acquisition unit 10, a light receiving unit 140 that includes a line sensor 142 and a drive circuit 143 that drives the line sensor 142, and an imaging acquired by the light receiving unit 140. A read signal processing unit 14 that performs signal processing such as AGC (Auto Gain Control), AOC (Auto Offset Control), and A / D conversion on the image, and processing by the read signal processing unit 14 And an image processing unit 40 that further performs color correction, gradation correction, and the like on the received signal.

  Each circuit block provided in the light receiving unit 140 and the read signal processing unit 14 is shown with reference elements R, G, B corresponding to the color components R, G, B. As the line sensor 142 for each color forming the light receiving unit 140, a CCD sensor (3-line color sensor) having a full width of 7500 pixels for each color is used. As shown by the side of the light receiving unit 140 in the figure, instead of the full width line sensor, m (for example, 4) ones having a width of 1 / m (for example, 1/4) with respect to the width in the main scanning direction. They may be used side by side in series.

  The read signal processing unit 14 provided at the subsequent stage of the light receiving unit 140 is a signal processing system corresponding to each image signal SR, SG, SB at a predetermined reading position imaged by the line sensor 142 for each color component, Each includes a sample hold circuit 244, an output amplifier circuit 246, an A / D conversion circuit 248, and a shading correction circuit 250.

  The central processing control unit 180 sets the driving cycle of the line sensor 142 by clocking the driving circuit 143, or controls the gain of the output amplifier circuits 246R, 146G, 146B and the shading correction circuits 250R, 250G, 250B. Control and so on. The drive circuit 143 and the central processing control unit 180 constitute a clock & pulse control unit 181.

  The line sensor 142 is driven by a drive signal from the drive circuit 143 to simultaneously read the positions separated by a predetermined distance of the original at each of the predetermined reading positions of the original, and each color component R, G at the reading position. , B corresponding to three systems of imaging signals SR, SG, SB (3-color analog video scanning line signals) are output.

  The imaging signals SR, SG, and SB are sampled by the corresponding sample and hold circuits 244 and then amplified to appropriate levels by the corresponding output amplifier circuits 246. At this time, the output amplifier circuit 246 performs gain offset adjustment, that is, signal processing such as AGC (Auto Gain Control) and AOC (Auto Offset Control). The signal output from the output amplifier circuit 246 is converted into digital image data DR, DG, and DB by the corresponding A / D conversion circuit 248, respectively.

  For these three systems of digital image data DR, DG, and DB, the corresponding shading correction circuit 250 performs correction with variations in pixel sensitivity of the corresponding line sensor 142 and brightness correction corresponding to the light quantity distribution characteristics of the reading optical system. The processed color data DR1, DG1, and DB1 are output to a synchronization processing unit (not shown) in the subsequent stage.

  The shading correction circuit 250 includes, for example, a subtraction circuit, a RAM (Random Access Memory) as a data holding unit, a multiplication circuit, a division circuit, and the like. As the RAM, for example, the line memory 251 may be prepared for each color (R, G, B).

  The shading correction circuit 250 performs white shading correction by, for example, performing normalization using the reading standard output of white reference data or black reference data in order to accurately read the image data of a document including halftones with multiple gradations. Or black shading correction (for example, see Japanese Patent No. 2629794, Japanese Patent No. 2658237, and Japanese Patent Laid-Open No. 7-143262).

  For example, a correction coefficient for each pixel (reciprocal of the white reference output) is generated based on the white reference read data, and the digital image data DR, DG, and DB as read image signals are multiplied. At this time, based on the address signal generated from the central processing control unit 180 that also performs the clock control of the CCD, the correction coefficient whose position is synchronized with the pixel to be corrected is sequentially read out from the line memory and normalized. Perform the operation.

  Thereby, for example, variations in the light amount of the light source, variations in sensitivity of each pixel of the imaging device (image sensor), variations in the dark output voltage due to dark current, and the like are corrected.

  However, since the number of gradations (bit width) of image data is increasing, especially when color imaging is considered, the scale of the image processing circuit increases accordingly. That is, the color image processing circuit is further increased in circuit scale and cost as compared with the monochrome image processing circuit, and this also applies to white shading correction and black shading correction. For example, as the number of gradations (bit width) of the image data increases, the capacity of the memory that stores the white reference data and the black reference data increases.

  An image processing unit 40 arranged at the subsequent stage of the read signal processing unit 14 is an in-plane position reference type color unevenness correction unit 410 which is a characteristic part of the present embodiment, and a known for faithfully reproducing the color of the document. An input tone correction unit 420 that performs END conversion (Equivalent Neutral Density) or ENL conversion (Equivalent Neutral Luminance), and device-independent image data using color correction matrix calculation And a standardized color correction unit (color correction matrix calculation unit) 430 that performs conversion to a standard output.

  In the configuration of the first embodiment, the color unevenness correction unit 410 is provided in a stage preceding the standardized color correction unit 430, that is, in an image processing path from reading an image to be read to converting it into standard color coordinate data. Characterized by points. The in-plane color unevenness correction in the main scanning direction by the color unevenness correction unit 410 and the standardized color correction for conversion to the standard output by the standardized color correction unit 430 are collectively referred to simply as color correction.

  The input tone correction unit 420 performs tone conversion processing with reference to the lookup table LUT, and passes the converted image data DR2, DG2, DB2 to the standardized color correction unit 430. In the END conversion, R, G, and B luminance data sent from the read signal processing unit 14 are converted into END data using a density function (see, for example, Japanese Patent Publication No. 6-101799). When converted into END data, when the original has a complete gray (achromatic) pattern, the R, G, and B values match to represent the monochrome density of the original. On the other hand, in the ENL conversion, R, G, and B reflectance (or transmittance) data sent from the read signal processing unit 14 is converted into a brightness signal using a brightness function (gamma conversion). Data is acquired (see, for example, paragraphs 0017, 26, 66-70, etc. of JP-A-7-143262 and FIG. 4).

  In the ENL conversion, as in the case of the END conversion, when the document has a complete gray (achromatic) pattern, the processing parameters are determined so that the R, G, and B values match. In END conversion, a density function is used as a function form, whereas in END conversion, only a lightness function is used as a function form. The input tone correction unit 420 of the present embodiment employs the latter ENL conversion.

  The standardized color correction unit 430 uses, for example, 3 × 10 three-color data as the R, G, B data to be processed using the image data DR2, DG2, DB2 subjected to the gradation conversion processing by the input gradation correction unit 420. By the matrix operation (matrix operation), the image data DR3, DG3, DB3 in the standard format, for example, are converted into Lab values expressed in a uniform color space that is standard color coordinates.

  The structure of color conversion using a look-up table and a matrix is described in paragraph 0017 of JP-A-7-143262. An example of matrix operation using 3 × 10 three-color data is disclosed in JP-A-5-300367. A constant term shown in paragraph 0034 of JP-A-7-322081 is added to what is shown in paragraph 0010 (see the following formula (1)). These examples are conversion to CMY, but adding higher-order terms is commonly used to improve the accuracy of matrix conversion, and the form of coefficients is common.

  Also, the conversion to sRGB (Standard RGB) value is also a γ characteristic of a lookup table (in the case of conversion to Lab, a conversion curve of approximately 1/3 power, because of the generality of matrix conversion, sRGB In the case of (2), the conversion curve is approximately 1 / 2.2), and the matrix coefficient can be changed in the same manner.

  In the image processing unit 40 according to the first embodiment, it is converted into a Lab value.

  When an image forming apparatus such as a copying machine or a multifunction machine is used, an image output device 950 is connected to the subsequent stage of the standardized color correction unit 430. The image output device 950 uses, for example, an electrophotographic method, a thermal method, a thermal transfer method, an ink jet method, or a similar conventional image forming process to display an image represented by an image signal obtained by the image input device 930. Thus, a visible image is formed (printed) on plain paper or thermal paper.

  Therefore, the image output device 950 operates as an image processing unit 952 that generates print output data such as binary signals of yellow Y, magenta M, cyan C, and black K, for example, and the image processing device operates as a digital printing system. A raster output scan-based print engine 954.

  The color unevenness correction unit 410, which is a characteristic part of the present embodiment, is based on the color data DR 1, DG 1, DB 1 sent from the read signal processing unit 14, which is read color information, and the read position information. In-plane color unevenness correction is performed.

  The “in-plane color unevenness in the main scanning direction” referred to here is an infrared cut filter that removes the influence of the dispersion of pixels in the spectral characteristics of the sensor used in the light receiving unit 140 and the infrared transmission region of the on-chip filter. This means color unevenness caused by variations in the light receiving sensitivity of the sensor due to the angle of view characteristics (particularly in the case of an interference film filter), that is, color unevenness due to variations in the light receiving sensitivity of each pixel in the main scanning direction.

  In addition, in place of the full width line sensor, when using 1 m of 1 / m width with respect to the width in the main scanning direction in series, there is a color step due to variation in light receiving sensitivity for each sensor. This color step itself is not included in the in-plane color unevenness which is a problem here.

  On the other hand, when the 1 / m-width m sensors are arranged in series and viewed as a full-width line sensor as a whole, the color unevenness caused by pixel variation in the light receiving sensitivity is “in-plane color unevenness in the main scanning direction”. Included. In this case, in the color unevenness correction process by the color unevenness correction unit 410, in-plane color unevenness is corrected for each of the n sensors (that is, each pixel). In this case, correction can be performed including absorption of color steps.

  It is important that the color unevenness correction unit 410 has little effect on gray (achromatic data). For this purpose, for example, the color unevenness correction unit 410 uses a function of difference between two color data (color difference function), and holds a coefficient (correction coefficient) for determining the color difference function for each position. A configuration may be employed (details will be described later).

  By using a correction coefficient for the data difference function between two colors (color difference function), it is possible to prevent the achromatic data from being affected, and the saturation between vivid colors and colors close to achromatic colors. Differences can also be taken into account. In this respect, similarly, color unevenness is obtained by performing gain correction only on a target single color using information on the color tone obtained from information on a plurality of read colors (color data of R, G, and B). This is different from the mechanism described in Japanese Patent Laid-Open No. Hei 6-152954 that performs correction.

  In order to reduce the amount of calculation data, it is preferable to employ a configuration in which a coefficient of power of the difference between two color data is held for each position (details will be described later). By making the correction coefficient a coefficient that is the difference between the data of the two colors, the amount of data necessary for correction can be minimized.

  In addition to the standardized color correction unit 430, the color unevenness correction unit 410 is provided as a functional unit that performs color unevenness correction, so that the read color data resulting from the spectral characteristics of the device (CCD in this example) of the light receiving unit 140 can be converted into the standard color. The function of converting to data (Lab, sRGB, etc.) and the function of correcting subtle unevenness of spectral characteristics in units of pixels can be separated. As a result, the color unevenness correction amount in the color unevenness correction unit 410 can be reduced, and the correction data amount can be reduced by realizing the correction operation with a small scale. In addition, the color unevenness correction amount can be determined with a small number of target colors.

  By correcting the color unevenness correction unit 410 so as not to affect the achromatic color data, errors caused by the correction can be minimized, and the color data that is greatly affected by the color unevenness is strongly corrected. The property can be realized.

  Hereinafter, the function of the color unevenness correction unit 410 which is a characteristic part of the present embodiment will be described in detail.

<Details of uneven color correction unit>
FIG. 4 is a functional block diagram illustrating a configuration example of the color unevenness correction unit 410 (also referred to as the color unevenness correction unit 410 of the first embodiment). The color unevenness correction unit 410 performs color correction by a matrix operation in units of positions and functions as a color correction matrix calculation unit in units of positions.

  Such an uneven color correction unit 410 uses Equation (2) as an example of a matrix operation so as to use a function of the difference between the two color data so as to hardly affect gray (achromatic color data). Apply. That is, gain correction is performed on the target single color and at least one other color (a total of at least two colors) of the three data of R, G, and B, and the original color data By performing the addition, color data corrected for color unevenness is acquired.

  For this reason, the color unevenness correction unit 410 includes a subtraction unit 412 and a product-sum operation unit 413, a correction calculation processing unit 414 that performs correction calculation processing related to color unevenness correction, and a color unevenness correction used by the correction calculation processing unit 414. And a correction coefficient storage unit 415 that stores the correction coefficient α related to each pixel.

  The subtraction unit 412 performs a difference process using any two color components of the input image data DR1, DG1, and DB1 for three colors. The product-sum operation unit 413 performs product-sum operation processing using the subtraction data Δ output from the subtraction unit 412, the input image data DR 1, DG 1, DB 1, and the correction coefficient α stored in the correction coefficient storage unit 415.

  The correction coefficient storage unit 415 can be constituted by a RAM as a data holding unit, for example. As the RAM, for example, a line memory 415 may be prepared for each color (R, G, B). For example, to realize the calculation according to the equation (2), the line memory 415_α11 is used for the correction coefficient α11 corresponding to the corrected data DBc, the line memory 415_α21 and the correction coefficient α22 are used for the correction coefficient α21 corresponding to the corrected data DGc. A line memory 415_α22 is prepared for the correction coefficient α31 corresponding to the corrected data DRc. Then, predetermined correction coefficients α11, α21, α22, and α31 are stored in association with the address position and pixel position of each line memory 415.

  In the correction coefficient storage unit 415, as described later, the characteristics of the color unevenness of the sensor to be used are checked in advance, and an appropriate correction coefficient α corresponding to the amount used in the product-sum operation according to the characteristics of the color unevenness. Is stored for each color and each pixel position. A predetermined inspection chart is used when obtaining the correction coefficient α. For example, a single color patch (difference in the density of each color material (primary color) of C, M, Y, K, which has been conventionally used for inspection of density reproducibility (or color reproducibility) of an electrophotographic color printing apparatus ( What is necessary is just to assume what arranged the small area | region of the uniform density | concentration in one dimension or two dimensions. A high-order single color patch in which two or more kinds of color materials are mixed may be included.

  The product-sum operation unit 414, when performing the matrix operation shown in Expression (2), based on the address signal generated from the central operation control unit 180, corrects the correction coefficients α11 to 11 that are synchronized with the correction target pixel. α31 is sequentially read from the correction coefficient storage unit 415.

  The product-sum operation unit 414 multiplies the read correction coefficients α11 to α31 by the outputs Δ11, Δ21, Δ22, and Δ31 of the subtraction unit 412 that obtains subtraction data between the two colors of the three color data, By adding the multiplication results as necessary, the difference data DΔB, DΔG, DΔR, that is, the correction term DΔ for the original data is acquired for each color, and the difference data DΔB, DΔG, DΔR and the original data DR1, DG1 are obtained. , DB1 is added to generate color data DRc, DGc, DBc on which color unevenness correction has been performed.

  5 to 7 are diagrams for explaining the problem of in-plane color unevenness in the main scanning direction. First, FIG. 5 shows an example of the spectral sensitivity characteristic of the CCD line sensor used in the light receiving unit 140. In this graph, the relative sensitivity of the photodetector (sensor) including the spectral characteristics of the filter is normalized as sensitivity 1 of the photodetector with the R filter and is shown as a distribution in the wavelength direction.

  For explanation, for the B color, in addition to the general characteristic indicated by the solid line B, a spectral response graph when a filter with low sensitivity, that is, a filter with a high filter density is provided, is indicated by a broken line B ′. Show.

  As shown in FIG. 5, the main cause of occurrence of in-plane unevenness of the read signal in the main scanning direction is that the spectral sensitivity bandwidth of the sensor changes due to uneven thickness of the on-chip filter. For this reason, at the base of the sensor spectral characteristics, the influence of unevenness in the reading surface becomes large for the color whose original color material spectral characteristics change.

  For example, when the broken line B 'is compared with the solid line B, there is a difference in relative sensitivity to the extent that it is close to the peak even at the base of the spectral response (near the wavelength of 500 nm). Therefore, the detection intensity of the component around the wavelength of 500 nm is greatly different between the photodetector with the filter having the characteristic of the solid line B and the photodetector having the filter with the characteristic of the broken line B ′. In other words, the spectral characteristic of the original color material changes in the vicinity of 500 nm corresponding to the bottom of the spectral band of the B color sensor, which is affected by the spectral characteristic unevenness of the B color sensor (hereinafter also referred to as a B channel sensor). A yellow or blue manuscript.

  Further, the influence of such filter density unevenness has a difference in spectral characteristics even with the same color material, and varies depending on the print density.

  FIG. 6 is a graph showing a reading result when an inspection chart with various densities is printed by using a certain Y color toner and the printed result is read by a photodetector with a B filter. . The horizontal axis of the graph is the reflectance value when the inspection chart is read with an ideal measuring instrument for measuring the reflectance of the B (blue) component, and this value is constant with the Y density of the inspection chart. Have a relationship. On the other hand, the vertical axis is a value obtained by converting the detection signal output from the photodetector with the B filter into reflectance. This graph shows a graph when the filter density of the B filter is changed from 0.6 to 1.4 in increments of 0.2. The filter density is normalized by setting the middle density value to 1.

  FIG. 7 is a diagram illustrating an example of reading value variation (error) due to filter variation. Here, the graph group in FIG. 6 is re-plotted with the vertical axis representing the error relative to the graph at the filter density of 1.0. That is, an example is shown in which the error of the reading reflectance value with respect to the filter density of the B channel sensor is simulated for the reflectance output of the B channel sensor for a yellow document. As can be seen from FIG. 7, the amount of error due to the filter density is proportional to the saturation of the yellow document, that is, the small B channel sensor output. In addition, it is affected by other colors that are spectrally adjacent.

  Therefore, as such saturation information, the product-sum operation correction coefficient α11 is provided for each pixel, the difference Δ11 (= DB1-DG1) between adjacent two color data is taken, and the difference Δ11 is multiplied by the correction coefficient α11. By applying correction to the original data DB1 using the multiplication result, it is possible to correct the spectral characteristic difference in units of pixels.

  Similarly, sensors for other colors have a product-sum operation correction coefficient α for each pixel, take a difference Δ between adjacent two-color data, multiply the difference by the correction coefficient α, and calculate the multiplication result. By using and correcting the original data, it is possible to correct the spectral characteristic difference in pixel units. For example, since the G channel sensor is spectrally adjacent to the R and B colors, it has correction coefficients α21 and α22 for each pixel, and the difference Δ21 (= DG1-DB1) and G between the G and B colors. The difference Δ22 (= DG1−DR1) between the color and the R color is taken, and the difference Δ21, Δ22 is multiplied by the corresponding correction coefficient α21, α22 to correct the original data DG1. Since the R channel sensor is spectrally adjacent to the G color, it has a correction coefficient α31 for each pixel and takes the difference Δ31 (= DR1−DG1) between the R color and the G color. The correction coefficient α31 is multiplied to correct the original data DR1.

  In addition, the cause of in-plane unevenness is caused by the angle-of-view characteristics of the infrared cut filter that removes the influence of the infrared transmission region of the on-chip filter (particularly in the case of an interference film filter). Also in this case, when the difference between two adjacent colors increases, the color unevenness increases, and therefore, it can be dealt with by the same correction. In any case, the color unevenness caused by the variation in the light receiving sensitivity of each pixel in the main scanning direction is corrected for what finally appears as the difference in the light receiving sensitivity of the pixels.

  Further, in such color unevenness correction processing according to the equation (2), the difference itself between the input color data is multiplied by the correction coefficient α, and correction is applied to the original data using the multiplication result. The correction accuracy can be further improved by utilizing the n (where n is a positive integer greater than or equal to 2) power term of the difference Δ.

  For example, regarding the B channel sensor, since the slopes of the spectral characteristics in the same 500 nm region are different between the blue and yellow color materials that are complementary to each other, for example, the difference Δ11 (= DB1-DG1) is negative and negative. In order to make the effect of the correction different depending on the case, it is conceivable to improve the correction accuracy by performing the correction taking up to the square term of the difference Δ11 (= DB1−DG1). Similarly, up to the square of the difference Δ21 (= DG1-DB1) and / or the difference Δ22 (= DG1-DR1) for the G channel sensor and the square of the difference Δ31 (= DR1-DG1) for the R channel sensor. Take up to the section. Since the dispersion of spectral sensitivity characteristics is larger at the base on the long wavelength side, it can be said that it is sufficient to use only the square term of the difference Δ22 (= DG1-DR1) for the G channel sensor.

  For the B channel sensor, in addition to the spectrally adjacent difference Δ11 (= DB1−DR1), in addition to the difference Δ11 (= DB1−DR1) in spectral characteristics, the difference Δ13 (= DB1) By including the term -DR1), the correction accuracy can be further improved.

  That is, it is conceivable to apply Equation (3) as an example of matrix calculation for improving the correction accuracy.

  In order to perform matrix calculation for improving the correction accuracy, the correction coefficient storage unit 415 uses the correction coefficients for the additional terms (α12, α13, α23, α32 in the case of following equation (3)) as the pixel position. For this purpose, for example, a run memory for each is prepared.

  However, even if the correction accuracy is increased in this way, it is only necessary to store 2 to 3 correction coefficients for each color for each pixel, and correction of in-plane spectral characteristic unevenness can be performed in units of pixels. it can.

  In this case, the data amount for the correction coefficient is about 2 to 3 times the amount of line memory used for shading correction, and does not give a large obstacle to the circuit scale.

  In addition, as a mechanism for improving the correction accuracy by taking a countermeasure against the sign of the subtraction data Δ, the previous example shows an example in which the square term of the subtraction data Δ is also used. However, the countermeasure is not limited to this. .

  For example, a method of determining the sign of the subtraction data Δ and switching the value of the correction coefficient α to be multiplied by the subtraction data Δ can be adopted. For example, it is conceivable to apply Equation (4) for the R channel sensor. Note that the correction coefficient α32 in equation (3) is different from the correction coefficient α32 in equation (4).

  Regardless of the equation (3) or (4), the correction amount DΔ for the original data is a function of the difference between the two colors, so that the correction amount is substantially “0” when reading achromatic colors. can do. When reading achromatic colors where correction errors are a concern, the difference between the two colors is almost “0”. For achromatic data that has been corrected with almost no in-plane unevenness by shading correction based on the normal white reference. Will not cause a correction error due to the addition of a new correction.

  In determining the correction term DΔ for correcting such in-plane unevenness in pixel units, first, Y (yellow), M (magenta), C (cyan), B (blue), G (green) , R (red) and other color materials of several kinds of color materials are used to read a chart with substantially uniform (uniform) density in the main scanning direction, and the average output in the main scanning direction for each color sensor and each pixel unit It is recommended to create difference data from Correction accuracy is improved by creating data that includes not only colors that are affected by unevenness (in the case of the B channel, Y and B colors that have a large wavelength change at the base of spectral sensitivity characteristics) but also those that are less affected by unevenness. It is to improve.

  At this time, similarly to the second embodiment described later, a band chart of a predetermined color having a uniform density in the main scanning direction is read, and pixel data at the same position in the main scanning direction is read in units of the band. It is preferable to create uneven print data in the main scanning direction by performing averaging processing in the sub-scanning direction to obtain pixel information at each main scanning position and creating difference data from the average output in the main scanning direction.

  Next, based on Equation (5), for example, the least square method is used so that the sum of the actual difference amount of each color and the difference data DΔ of each color in Equation (5) is minimized. The correction coefficient α may be obtained for each sensor and pixel.

  At this time, since the role of the color correction unit in units of pixels is limited to the correction with small variations for each pixel, the correction amount can be reduced compared to the correction amount at the time of conversion to the standard color. . In other words, non-linear conversion required when correcting the spectral characteristics of the entire reading system during conversion to standard colors does not need to be handled by pixel-by-pixel correction, and correction coefficients are determined for several hundred colors. Even if not, the correction coefficient may be determined based on a small number of colors such as YMCBGR. Originally, for achromatic colors and colors with low brightness, the amount of correction is small, so there is little need to use it for optimization.

  Strictly speaking, the correction coefficient needs to be changed depending on not only the saturation of the read color but also the spectral characteristics of the read color material (for example, a shift in the absorption wavelength due to the color material for printing and the color material for photography). In applications where output unevenness is measured, there is no need to consider color material differences because toner color materials used in printers are limited.

  As described above, according to the configuration of the image acquisition unit 10 of the first embodiment, particularly the image processing unit 40 which is a signal processing system related to color correction (in-plane color unevenness correction and standardized color correction in the main scanning direction). A correction function for in-plane color unevenness in the main scanning direction due to variations in the on-chip filter characteristics in the pixel column direction (main scanning direction) of the imaging device used by the light receiving unit 140 and the field angle characteristics of the optical system spectral characteristics. To achieve this, the standardized color correction unit 430 that realizes the function of converting to standard color data (Lab in the previous example), and the color unevenness that realizes the function of correcting color unevenness caused by subtle variations in spectral characteristics in units of pixels. Separated from the correction unit 410.

  That is, during the process of converting the raw read data that has only been standardized by the white reference into the reference output (Lab value in this example), that is, in the process of converting to the standard color coordinate data after shading correction, the correction amount The color unevenness correction is performed in units of small pixels, and two color correction units that perform conversion to reference output coordinates where the correction amount is relatively large are provided.

  In particular, for the color unevenness correction function, for example, for each color data to be corrected such as R, G, B color data, that is, for each color to be corrected, the target single color and at least one other color are combined. Thus, by correcting the data of at least two colors, the color data corrected for color unevenness is obtained.

  As a result, both functions of correcting in-plane color unevenness in the main scanning direction and correcting conversion to standard color coordinate data can be achieved with a relatively simple configuration. For example, by correcting unevenness in the reading surface due to on-chip filter unevenness of the sensor and spectral field angle characteristics of the optical system, color reading characteristics with accuracy that can be used for in-plane unevenness measurement of print output are obtained. In addition, the amount of correction data necessary for the in-plane color unevenness correction function can be realized on a realistic scale.

  For example, it is possible to ensure the reading accuracy required for detecting the print output unevenness of a digital copying machine. Further, the correction amount in the color unevenness correction unit 410 can be reduced. As a result, color unevenness correction can be realized with a small-scale correction calculation, and the amount of correction data can be reduced.

  In addition, the amount of correction for correcting uneven color can be determined with a small number of target colors, and by performing arithmetic processing that does not affect achromatic data, errors caused by correction can be minimized. In addition, it is possible to realize a property in which correction is strongly applied to chromatic data that is greatly affected by color unevenness.

<Comparison with other configuration examples>
For example, in standard scanner reading, in-plane unevenness correction and color reading characteristics correction can be done by pixel-based white reference (some methods add black reference correction), or the entire reader It can be considered that the conversion to the standard output using the color correction matrix operation is performed.

  In this case, for example, in the signal processing system of the image acquisition unit 10 of the present embodiment illustrated in FIG. 3, it is possible to adopt a configuration in which the color unevenness correction unit 410 is removed. The signal flow in this case is as follows. The analog video scanning line signals SR, SG, and SB output from the line sensor 142 are subjected to gain offset adjustment on the analog signal by the output amplifier circuit 246 and then A / D conversion circuit 248 performs A / D conversion. D-converted and converted into digital signals DR, DG, DB.

  Thereafter, the shading correction circuit 250 performs normalization using the read standard output of the white reference data. Here, the data DR1, DG1, and DB1 after shading correction are performed by multiplying a correction coefficient (reciprocal of the white reference output) for each pixel generated based on the white reference read data and the read image signal. The data is output to the processing unit 40. At this time, the correction coefficient whose position is synchronized with the pixel to be corrected is sequentially read out from the line memory 251 by the address signal generated from the central processing control unit 180 that also controls the clock of the CCD. Normalization operations are performed.

  Next, in the image processing unit 40, after the image data DR 2, DG 2, and DB 2 are obtained by performing gradation conversion processing by LUT called ENL conversion in the input gradation correction unit 420, the standardized color correction unit At 430, the image data DR3, DG3, and DB3 in the Lab color space or sRGB color space, which are standard color coordinates, are converted by matrix calculation using 3 × 10 three-color data.

  Here, when an image is read using the line sensor 142 having a plurality of pixels in the main scanning direction, the image is read due to variations in the thickness of the on-chip filter provided on the pixels of the line sensor 142, the angle of view characteristics of the optical system, and the like. There is unevenness in the main scanning direction in the spectral characteristics, and as a result, unevenness in brightness occurs in the main scanning direction on the output image. What is improved is so-called shading correction.

  However, as described above, the general shading correction processing is performed only for the normalization calculation based on the white reference, and only the lightness unevenness correction in R, G, B color units. Regarding the color generated by the combination of B, color unevenness remains due to a subtle difference in brightness unevenness of the three colors. In other words, it is not possible to deal with in-plane color unevenness only by general shading correction processing. When a highly saturated color is read, color unevenness exists in the main scanning direction on the output image.

  However, in applications such as conventional color digital copiers, the in-plane color unevenness caused by such dispersion in spectral characteristics is large compared to the in-plane variation in the output of the color laser printer that constitutes the copier, so it is large. It can be said that it does not matter. In other words, in conventional copying applications, the in-plane color unevenness on the image forming apparatus side is larger than the in-plane color unevenness on the reading apparatus side. Color unevenness is not a problem.

  However, on the other hand, in order to apply a color laser printer to the printing market, improvement of in-plane unevenness on the image forming apparatus side is progressing. When image quality is improved on the image forming apparatus side, in-plane color unevenness on the reading apparatus side, which has not been a problem in the past, will be noticed.

  Also, as a function of the reading unit of a digital copying machine, in addition to a reading device for a copying machine and a scan-in terminal, the use of calibration of output characteristics between color printers and in-plane unevenness detection of color printers is also considered. . In such applications, a color difference of about “1” is required as in-plane reading unevenness. Therefore, in such applications, the problem of in-plane color unevenness due to variations in in-plane spectral characteristics as described above becomes obvious.

  In addition, it is conceivable to reduce the interval between the read pixel columns in order to improve the three-color registration error. However, this technology flow makes it difficult to accurately form an on-chip filter in each read pixel column. The spectral characteristic variation performance is hindered. As a result, on the reading device side, the three-color registration error improvement and the in-plane color unevenness are in opposite directions.

  Various proposals have been proposed for correcting color unevenness caused by such variations in spectral characteristics. Note that color correction in a color copying machine is one that corrects spectral characteristic differences caused by the reading device using color correction coefficients and converts them into standard color coordinates such as Lab and sRGB (standard characteristic conversion). In some cases, the standard color coordinate is converted into a YMCK signal output from the printer. Here, the former is targeted.

  Conventionally, a small matrix of about 3 × 4 should be used as the color correction coefficient, but in order to obtain the color conversion accuracy, a quadratic term of the read color such as 3 × 10 or 3 × 20 Use third-order terms.

  For this reason, if it is assumed that the color correction coefficients for the standard output have 3 × 10 coefficients (30) for all pixels, the amount of memory becomes enormous. In addition, when one color correction unit (color conversion unit) tries to play two roles of in-plane color unevenness correction and standard characteristic conversion, since the conversion to the standard characteristic has strong nonlinear conversion characteristics, Due to the difference in the conversion characteristics, it may be assumed that new unevenness occurs in pixel units or small block units.

  In order to determine such a color correction coefficient, an optimum value is usually obtained by using data of several hundred colors. However, if this is performed for each pixel unit, a huge amount of man-hours are required and several tens of sheets are required. Due to fluctuations during the collection of the corrected output data, there is a concern that accuracy may be reduced.

  As another mechanism for correcting color unevenness caused by spectral characteristic unevenness in the main scanning direction, there is a mechanism described in Japanese Patent Laid-Open No. 6-152594. In this mechanism, a functional unit for correcting color shading (synonymous with color unevenness) is further provided for image data subjected to white shading. Specifically, the spectral distribution was measured to determine what color tone the white-shaded image was, and white shading was applied to reduce the unevenness of the color tone based on the measurement result. With respect to each color data of R, G, and B, correction is made for each element constituting the sensor while referring to the pixel address. That is, R (G, B) data with corrected color unevenness is obtained by performing gain correction with reference to the color tone on any one of R, G, and B data subjected to white shading correction.

  Since the color tone is determined by information of a plurality of read colors, the color shading is corrected by correcting the output data of each element constituting the sensor based on the result of measuring the color tone. The basic function of the color unevenness correction unit 410 of this embodiment that performs color unevenness correction using R, G, and B color data, which is information on a plurality of read colors, and information on read positions is similar.

  However, in the present embodiment, R (G, B) data obtained by correcting color unevenness by applying correction using color difference information that is a difference between two colors, that is, three of R, G, B R (G, B) data with corrected color unevenness is obtained by performing gain correction on the target single color and at least one other color (in combination, at least two colors) of the data. Therefore, the correction calculation (for example, matrix calculation) using data of a plurality of colors for each target color is performed, and color unevenness correction in consideration of both hue and saturation can be performed.

  As a result, it is possible to take into account the difference between a brightly saturated color and a color close to an achromatic color, and correction can be made with an appropriate amount corresponding to the difference in saturation. The information of only the color tone is greatly different from the case where correction cannot be made with an appropriate amount corresponding to the difference in saturation.

  In addition, the applicant of the present application has proposed a mechanism for determining a color shading coefficient in Japanese Patent Application No. 2005-020991, limited to reading of a test chart. In this mechanism, it is necessary to have correction data for each of R, G, and B colors, and only a limited color can be handled. On the other hand, in the present embodiment, not only R, G, and B to be corrected but also color information held as correction data, for example, Y, M, and C, considering gain correction for color difference data. Therefore, compared with the case where correction data is provided only for R, G, and B to be corrected, the range in which color unevenness can be improved is widened.

<Signal Processing System of Image Acquisition Unit; Second Embodiment>
FIG. 8 is a block diagram showing a second embodiment in detail focusing on the signal processing function of the image acquisition unit 10.

  The second embodiment is characterized in that a color unevenness correction unit 440 is provided outside the processing circuit constituting the image acquisition unit 10 and the color unevenness correction unit 440 arranged outside the color correction is performed.

  From this point of view, it can be realized with almost no hardware change to the conventional configuration. For example, in the process until the color data of a predetermined color space representing the read image is converted into the standard color coordinate data, that is, from the output of the read signal processing unit 14 to the input to the standardized color correction unit 430, the image processing unit 40. A configuration may be adopted in which image data is taken into an external color unevenness correction unit 440 from the middle of the data path, and the image data is corrected after color unevenness correction and then returned. Under the restriction of “in the previous stage of the standardized color correction unit 430”, the image data is actually captured immediately before or immediately after the input tone correction unit 420, and the image data after the color unevenness correction is returned. .

  The implementation of the color unevenness correction function outside is not limited to the use of the color unevenness correction unit 440 configured by a dedicated hardware circuit, and personal data is used using data captured from the middle of the data path in the image processing unit 40. It can also be realized by performing arithmetic processing by an electronic computer such as a computer (personal computer). That is, the electronic computer implements the function of the color unevenness correction unit 440 by software processing. In the following, the description will focus on differences from the configuration of the first embodiment shown in FIG.

  For example, the color unevenness correction unit 440 includes the image processing unit 40 in addition to the correction calculation processing unit 444 corresponding to the correction calculation processing unit 414 and the correction coefficient storage unit 445 corresponding to the correction coefficient storage unit 415 of the first embodiment. A data holding unit 449 for holding image data (image data representing a read image) captured from the middle of the data path is prepared. Then, color unevenness correction may be performed by the correction calculation processing unit 444 on the image data stored in the data holding unit 449 or image data after performing desired signal processing as necessary.

  FIG. 9 is a diagram illustrating an example of a chart used when measuring print density unevenness using a reading unit that reduces unevenness in the reading surface by using such correction processing. As shown in the figure, C, M, Y, and K color materials (primary) used for inspection of density reproducibility (or color reproducibility) used in an image forming unit (image output unit; print engine). Color) (and higher order colors if necessary) are monochromatic patches (small areas of uniform density) of different densities arranged in the main scanning direction, that is, one-dimensionally.

  In this way, strip regions B_1, B_2,..., B_M (M is positive) having the width of the print range in the main scanning direction of the print engine with different densities of each primary color (and higher order colors if necessary). By using an inspection chart (band chart) including an integer (showing up to 5 in the figure), in addition to density reproducibility, printing density unevenness (in-plane unevenness) in the main scanning direction can be inspected. If the number of colors to be inspected is too large to fit on a single inspection chart, printing is performed separately for a plurality of sheets. In FIG. 9, the difference in color is expressed by the difference in hatching pattern.

  In the color unevenness correction unit 440 of the second embodiment, in order to perform the color unevenness correction process, for example, the same as shown in FIG. 9, a strip chart of a predetermined color having a flat (uniform) density in the main scanning direction. The pixel data at the same position in the main scanning direction is averaged in the sub scanning direction as pixel information at each main scanning position, that is, converted into color information in color band units. It is preferable to create print output unevenness data in the main scanning direction based on difference data from the average output in the main scanning direction, and obtain a correction coefficient α for correcting color unevenness based on the information.

  In principle, it is possible to obtain the correction coefficient α based only on image data of one main scanning line. However, if variation in reading is taken into consideration, a plurality of correction coefficients α are provided for each same pixel position in the main scanning direction. If the pixel information at each main scanning position is acquired based on the average value of the information (pixel data) obtained at the sub-scanning position, the accuracy is remarkably improved.

  Even in the color unevenness correction by the configuration and method of the second embodiment as described above, in the middle of the process of converting the raw read data that has only been standardized by the white reference to the reference output (Lab value or sRGB value), that is, A functional unit that performs color unevenness correction for each pixel in the main scanning direction with a small correction amount based on color information (difference data between two colors as described above) in the process of conversion to standard color coordinate data after shading correction. In addition, the configuration having two color correction units such as a function unit that performs conversion to a reference output coordinate with a relatively large correction amount is the same as the first embodiment described above, and in-plane color unevenness. The effect obtained with respect to the correction is basically the same as that of the first embodiment.

<Signal Processing System of Image Acquisition Unit; Third Embodiment>
FIG. 10 is a block diagram showing a third embodiment in detail focusing on the signal processing function of the image acquisition unit 10.

  This third embodiment is characterized in that color unevenness correction is performed after the standardized color correction. Specifically, a color unevenness correction unit 450 is provided in the subsequent stage of the standardized color correction unit 430. Such a configuration including the color unevenness correction unit 450 subsequent to the standardized color correction unit 430 can be realized without changing the hardware of the conventional configuration. For example, output data from the standardized color correction unit 430 This can also be realized by performing arithmetic processing using an electronic computer such as a personal computer. That is, the electronic computer implements the function of the color unevenness correction unit 450 by software processing. In the following, the description will focus on differences from the configuration of the first embodiment shown in FIG.

  First, the standardized color correction unit 430 in the image processing unit 40 according to the third embodiment uses the ENL converted image data output from the input tone correction unit 420 as R, G, B data to be processed, for example, 3 Conversion into sRGB values as standard format data is performed by matrix calculation (matrix calculation) using three-color data of × 10.

  The color unevenness correction unit 450 arranged at the subsequent stage of the standardized color correction unit 430 is a gradation correction unit that performs gradation conversion (also referred to as reverse gradation conversion) with a reverse characteristic to the gradation conversion in the input gradation correction unit 420. 453, the correction coefficient processing unit 454 having the same configuration as the correction calculation processing unit 414 in the color unevenness correction unit 410 of the first embodiment, and the correction coefficient storage unit 455 having the same configuration as the correction coefficient storage unit 415, and the correction calculation processing A gradation correction unit 457 that performs gradation conversion of the same characteristics as the gradation conversion in the input gradation correction unit 420 on the image data that has been subjected to color unevenness correction by the unit 454; As the reverse gradation conversion and gradation conversion in the gradation correction units 453 and 457, ENL conversion is adopted as in the input gradation correction unit 420 of the first embodiment.

  In the case of the configuration of the third embodiment, since the gradation correction unit 453 performs reverse gradation correction once and then performs color unevenness correction, and then the gradation correction unit 457 performs gradation correction. The order in which color unevenness correction processing in the scanning direction is performed is practically the previous stage of ENL correction, as in the first embodiment.

  For example, image data DR3, DG3, DB3 represented by standard color coordinates (sRGB color space in this example) output from the standardized color correction unit 430 is taken into a personal computer and color unevenness correction is performed in the main scanning direction.

  Here, in order to apply the color unevenness correction process to the image data DR3, DG3, DB3 output as the standard output sRGB data in the reflectance space, the effect of the gradation correction by the input gradation correction unit 420 is based on the original. Pixel unit in the main scanning direction performed by the correction calculation processing unit 414 of the first embodiment based on the image address determined at the time of taking in the image data after performing the inverse ENL conversion by the gradation correction unit 453 to return to The color unevenness correction processing is performed by software processing, and the ENL conversion is performed again by the gradation correction unit 457, thereby converting the image data into the image data DR4, DG4, and DB4 expressed in standard color coordinates (sRGB color space in this example). To do.

  The image data DR4, DG4, and DB4 generated in this way are used for, for example, calculation of color patch data in calibration of output characteristics between color printers, and extraction of color unevenness information at the time of print output in a color printer. In addition, it is suitable for obtaining highly accurate output image data.

<Signal Processing System of Image Acquisition Unit; Fourth Embodiment>
FIG. 11 is a block diagram showing a fourth embodiment in detail focusing on the signal processing function of the image acquisition unit 10. FIG. 12 is a diagram illustrating processing of one functional unit in the color unevenness correction unit according to the fourth embodiment.

  The fourth embodiment is the same as the third embodiment in that color unevenness correction is performed after the standardized color correction. However, the fourth embodiment uses standard color coordinates (sRGB color space in this example) output from the standardized color correction unit 430. Using the represented image data DR3, DG3, and DB3 as a processing target, once averaging processing for a predetermined number of lines in the sub-scanning direction is performed, a numerical data string in the sub-scanning direction is generated, and inverse ENL correction is performed. It is characterized in that the in-plane color unevenness correction in the main scanning direction is corrected.

  Specifically, a color unevenness correction unit 460 including the same components as the color unevenness correction unit 450 of the third embodiment is provided after the standardized color correction unit 430. Note that the configuration including the color unevenness correction unit 460 subsequent to the standardized color correction unit 430 can also be realized by performing arithmetic processing using an electronic computer such as a personal computer, as in the third embodiment. That is, the electronic computer implements the function of the color unevenness correction unit 460 by software processing. Hereinafter, the difference from the configuration of the third embodiment illustrated in FIG. 10 will be mainly described.

  First, the gradation correction unit 463 is the gradation correction unit 453, the correction calculation processing unit 464 is the correction calculation processing unit 454, the correction coefficient storage unit 465 is the correction coefficient storage unit 455, and the gradation correction unit 467 is the gradation correction. Each corresponds to the portion 457.

  Further, as a characteristic part of the color unevenness correction unit 460 of the fourth embodiment, main scanning is performed in units of band data corresponding to a predetermined number of lines in the sub-scanning direction of the image data DR3, DG3, DB3 captured from the standardized color correction unit 430. A sub-scanning direction averaging processing unit 461 that averages pixel data at the same position in the direction in the sub-scanning direction, and an average output at each position in the main scanning direction subjected to the averaging process is output every predetermined number of lines. And a numerical data string processing unit 462 for converting into numerical data strings in the sub-scanning direction, that is, color information in units of color bands.

  Here, the “predetermined number of lines” is preferably the number of lines corresponding to a strip-shaped chart of a predetermined color having a flat (uniform) density in the main scanning direction as shown in FIG.

  In the color unevenness correction unit 460 of the fourth embodiment as described above, from the read image data of the sRGB coordinates, as shown in FIG. 12, a predetermined number of lines in the sub-scanning direction are once associated with the belt-like region of the belt-like chart. Is processed by the sub-scanning direction averaging processing unit 461, and then output as a numerical data sequence by the numerical data sequence processing unit 462. Hereinafter, as in the third embodiment, the color unevenness correction processing is performed with the reflectance. In order to apply in space, the tone correction unit 463 performs inverse ENL conversion in order to restore the effect of the tone correction by the input tone correction unit 420. Thereafter, based on the image address determined when the image data is taken in, the color unevenness correction processing for each pixel in the main scanning direction, which has been performed by the correction calculation processing unit 414 of the first embodiment, is performed, and the gradation correction unit 457 performs. By performing the ENL conversion again, it is output as a numerical data string DR5, DG5, DB5 expressed in standard color coordinates (sRGB color space in this example).

  The numerical data strings DR5, DG5, and DB5 generated in this way can be used as they are as in-plane color unevenness data in the main scanning direction of the printer to be inspected.

<Signal Processing System of Image Acquisition Unit; Fifth Embodiment>
FIG. 13 is a block diagram showing a fifth embodiment in detail focusing on the signal processing function of the image acquisition unit 10. FIG. 14 is a diagram illustrating processing of one functional unit in the color unevenness correction unit according to the fifth embodiment.

  The fifth embodiment is the same as the third and fourth embodiments in that color unevenness correction is performed after the standardized color correction. First, the standardized color correction unit 430 uses a coefficient of a 3 × 10 color correction matrix portion. Is set to a coefficient that makes processing easy, and after color unevenness correction, standardized color correction using color correction matrix processing is performed. The basic signal processing before and after color unevenness correction is the same as in the fourth embodiment.

  Specifically, a color unevenness correction unit 470 including the same components as the color unevenness correction unit 460 of the fourth embodiment is provided after the standardized color correction unit 430. Note that the configuration including the color unevenness correction unit 470 subsequent to the standardized color correction unit 430 can also be realized by performing arithmetic processing using an electronic computer such as a personal computer, as in the third and fourth embodiments. That is, the electronic computer realizes the function of the color unevenness correction unit 470 by software processing. Hereinafter, the difference from the configuration of the fourth embodiment shown in FIG. 11 will be mainly described.

  First, the sub-scanning direction averaging processing unit 471 performs correction in the sub-scanning direction averaging processing unit 461, the numerical data string processing unit 472 in the numerical data string processing unit 462, and the gradation correction unit 473 in the gradation correction unit 463. The arithmetic processing unit 474 corresponds to the correction arithmetic processing unit 464, the correction coefficient storage unit 475 corresponds to the correction coefficient storage unit 465, and the gradation correction unit 477 corresponds to the gradation correction unit 467.

  As a characteristic part of the color unevenness correction unit 470 of the fifth embodiment, first, a main scanning direction averaging processing unit 476 is provided between the correction calculation processing unit 474 and the gradation correction unit 477. The main scanning direction averaging processing unit 476 performs averaging processing for a predetermined number of pixels in the main scanning direction on the image data DRc, DGc, DBc subjected to color unevenness correction by the correction calculation processing unit 474.

  Here, the “predetermined number of pixels” is the number of pixels in the main scanning direction corresponding to a rectangular chart of a predetermined color having a flat (uniform) density in the main scanning direction and the sub-scanning direction as shown in FIG. It is good to do.

  Note that the “predetermined number of lines” to be averaged in the sub-scanning direction averaging processing unit 471 is a predetermined color having a flat (uniform) density in the main scanning direction and the sub-scanning direction as shown in FIG. It is preferable to set the number of pixels (number of lines) in the sub-scanning direction corresponding to a rectangular chart.

  Further, as a characteristic part of the color unevenness correction unit 470 of the fifth embodiment, a standardized color correction unit 478 having a function similar to that of the standardized color correction unit 430 is provided after the gradation correction unit 477. In this example, it is converted to data in the Lab color space. The color unevenness correction unit 470 that performs color unevenness correction for each pixel in the main scanning direction with a small correction amount based on the color information (difference data between the two colors as described above) effectively has a relatively large correction amount. This is a configuration including a color correction unit that performs conversion into reference output coordinates.

  FIG. 15 is a diagram illustrating an example of an image (patch chart) used for color unevenness correction in the color unevenness correction unit 470 according to the fifth embodiment. As shown in the figure, C, M, Y, and K color materials (primary) used for inspection of density reproducibility (or color reproducibility) used in an image forming unit (image output unit; print engine). Color) (and higher order colors if necessary) are monochromatic patches (small areas of uniform density) with different densities arranged in the main scanning direction and the sub-scanning direction, that is, two-dimensionally.

  In this way, the rectangular areas B_11, B_12,..., B_1M having the widths of the print ranges in the main scanning direction and the sub-scanning direction of the print engine having different densities of the primary colors (and higher order colors if necessary) By using an inspection chart (rectangular chart) including B_21, B_22,..., B_2M,..., B_N1, B_N2, ..., B_NM (M and N are positive integers), in addition to the density reproducibility, the main scanning direction In addition, the printing density unevenness (in-plane unevenness) in the sub-scanning direction can be inspected. If the number of colors to be inspected is too large to fit on a single inspection chart, printing is performed separately for a plurality of sheets. In FIG. 15, the difference in color is expressed by the difference in hatching pattern.

  In order to perform the color unevenness correction process in the color unevenness correction unit 470 of the fifth embodiment, first, as a premise, the coefficient of the 3 × 10 color correction matrix portion in the standardized color correction unit 430 is set to a coefficient that facilitates the process. To do. Therefore, in effect, the standardized color correction unit 430 outputs device-dependent RGB coordinate image data DR 6, DG 6, and DB 6 that have undergone only ENL correction by the input tone correction unit 420.

  Then, for example, as shown in FIG. 15, a rectangular portion (in particular, also called a test patch) of a predetermined color having a flat (uniform) density in the main scanning direction and the sub-scanning direction is read. In the sub-scanning direction averaging processing unit 471, pixel data at the same position in the main scanning direction is averaged in the sub-scanning direction to obtain pixel information at each main scanning position. And is output as a numerical data string by the numerical data string processing unit 472.

  Then, in order to apply the color unevenness correction process in the reflectance space, the tone correction unit 473 performs inverse ENL conversion to restore the effect of the tone correction by the input tone correction unit 420. Thereafter, based on the image address determined at the time of image data fetching, the color unevenness correction processing for each pixel in the main scanning direction, which has been performed by the correction calculation processing unit 414 of the first embodiment, is performed.

  Thereafter, in the main scanning direction averaging processing unit 476, as shown in FIG. 14B, the numerical value at the same position in the sub-scanning direction corresponding to the rectangular area (patch range) in the main scanning direction of the patch chart. The column data is averaged in the main scanning direction to obtain pixel information at each sub-scanning position, that is, converted to color information in the main scanning direction unit of the test patch. As shown in FIG. 14A, the sub-scanning direction averaging processing unit 471 performs averaging processing in correspondence with the rectangular area (patch range) in the sub-scanning direction of the patch chart, and the numerical data string processing unit 472 As a result, the color information (numerical string data) in the sub-scanning direction unit of the test patch is converted into color information in color patch units.

  Further, after ENL conversion is performed again by the gradation correction unit 477, the standardized color correction unit 478 performs 3 × 10 color correction matrix processing in the same manner as the standardized color correction unit 430 of the first embodiment. Thus, it is output as numerical data DR7, DG7, DB7 expressed in standard color coordinates (Lab color space in this example). As a result, color coordinate information for each Lab color patch is output.

  The numerical data DR7, DG7, and DB7 generated in this way are used for grasping in-plane color unevenness data in the main scanning direction of the printer to be inspected and color output characteristics between the printers, as in the fourth embodiment. It can be used as it is as more accurate data.

  In the color unevenness correction according to the configurations and methods of the third to fifth embodiments, standard color coordinate data is output at the final stage of processing regardless of image data or numerical data. In other words, in the middle of the process of converting the read raw data that has only been standardized by the white reference into the reference output (Lab value or sRGB value) and outputting it, that is, after the shading correction, it is converted to the standard color coordinate data and output. In this process, a functional unit that performs color unevenness correction for each pixel in the main scanning direction with a small correction amount based on color information (difference data between two colors as described above), and a reference for a relatively large correction amount Having a configuration having two color correction units called function units that perform conversion to output coordinates is the same as in the first embodiment described above, and basically the effects obtained with respect to in-plane color unevenness correction are also obtained. There is no difference from the first embodiment.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in each of the above-described embodiments, the correction characteristic is a linear characteristic with respect to the reflectance as shown in FIG. 7, and thus correction in the reflectance space is desirable. The order of performing the in-plane color unevenness correction process in the direction is the previous stage of the ENL correction.

  However, it is not essential to perform color unevenness correction before the ENL correction, and even if color unevenness correction is performed after the ENL correction, a corresponding correction effect can be obtained.

<Configuration using an electronic computer>
As described above, the series of image processing functions in the image processing unit 40 including the color unevenness correction function described above can be executed by hardware, but can also be executed by software. That is, each functional unit related to execution of image processing (particularly image processing related to color correction) is not limited to being configured by hardware, but uses an electronic computer (computer) based on a program code that realizes the function. It can also be realized in software. For example, similarly to the configuration of a general PC (personal computer) main body, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read-Only Memory), and the like can be provided.

  The execution of the image processing described above can be realized by the CPU executing an application program incorporated in the image processing apparatus having this computer configuration. Therefore, an image processing program suitable for realizing the image processing method and apparatus according to the present invention by software using an electronic computer (computer) or a computer-readable storage medium storing the image processing program is extracted as an invention. You can also

  Of course, the configuration is not limited to such a computer, but may be configured by a combination of dedicated hardware that performs each function. By adopting a mechanism for executing processing by software, it is possible to enjoy the advantage that the processing procedure, processing conditions, and the like can be easily changed without changing hardware. On the contrary, if it is configured by hardware, high-speed processing can be realized.

  The recording medium causes a state change of energy such as magnetism, light, electricity, etc. according to the description contents of the program to the reading device provided in the hardware resource of the computer, and in the form of a signal corresponding to the change. The program description can be transmitted to the reader.

  For example, a magnetic disc (including a flexible disc), an optical disc (CD-ROM (Compact Disc-Read Only Memory)), a DVD (which is distributed to provide a program to a user separately from a computer, (Including Digital Versatile Disc), magneto-optical disc (including MD (Mini Disc)), or package media (portable storage media) made of semiconductor memory, etc. It may be configured by a ROM, a hard disk, or the like in which a program is recorded that is provided to the user in a state. Or the program which comprises software may be provided via communication networks, such as a wire communication or radio | wireless.

  When a series of image processing (especially image processing related to color correction) is executed by software, a computer (an embedded microcomputer or the like) in which a program constituting the software is incorporated in dedicated hardware, a CPU, Various functions can be executed by installing a system on a chip (SOC) that implements a desired system by mounting functions such as logic circuits and storage devices on a single chip, or by installing various programs. It is installed from a recording medium in a general-purpose personal computer capable of doing so.

  For example, a storage medium storing software program codes for realizing an image processing function is supplied to a system or apparatus, and a computer (or CPU or MPU) of the system or apparatus reads and executes the program code stored in the storage medium By doing so, the same effect as that achieved by hardware can be achieved. In this case, the program code itself read from the storage medium realizes the image processing function.

  Further, not only the function of performing image processing is realized by executing the program code read by the computer, but also an OS (operating system; basic software) running on the computer based on an instruction of the program code May perform a part or all of the actual processing and realize a function of performing image processing by the processing.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. There may be a case where the CPU or the like provided in the card or the function expansion unit performs part or all of the actual processing, and the function of performing image processing is realized by the processing.

  In such an electronic computer, for example, software similar to that in a conventional image forming apparatus (multifunction machine) such as a copying application, a printer application, a facsimile (FAX) application, or a processing program for other applications is incorporated. . A control program for transmitting and receiving data to and from the outside via the network 9 is also incorporated.

  At this time, the program is provided as a file describing a program code that realizes a function of performing image processing. In this case, the program is not limited to being provided as a batch program file, and the hardware of the system configured by a computer Depending on the configuration, it may be provided as an individual program module. For example, it may be provided as add-in software incorporated in existing copying apparatus control software or printer control software (printer driver).

  FIG. 16 shows a case where an image processing apparatus corresponding to the image processing unit 40 is configured by software using a CPU and a memory, that is, an image processing apparatus is realized by software using an electronic computer such as a personal computer. It is the figure which showed an example of the hardware constitutions.

  A computer system 900 constituting an image processing apparatus receives data from a controller 901 and a predetermined storage medium such as a hard disk device, a flexible disk (FD) drive, a CD-ROM (Compact Disk ROM) drive, a semiconductor memory controller, or the like. And a recording / reading control unit 902 for reading and recording.

  The controller unit 901 includes a CPU (Central Processing Unit) 912, a ROM (Read Only Memory) 913 which is a read-only storage unit, and a RAM (Random Access) which can be written and read at any time and is an example of a volatile storage unit. Memory) 915 and RAM (described as NVRAM) 916 which is an example of a nonvolatile storage unit.

  In the above description, the “volatile storage unit” means a storage unit in a form in which the stored contents are lost when the power of the image output terminal 4 is turned off. On the other hand, the “nonvolatile storage unit” means a storage unit in a form that keeps stored contents even when the main power supply of the apparatus is turned off. Any memory device can be used as long as it can retain the stored contents. The semiconductor memory device itself is not limited to a nonvolatile memory device, and a backup power supply is provided to make a volatile memory device “nonvolatile”. You may comprise as follows. Further, the present invention is not limited to a semiconductor memory element, and may be configured using a medium such as a magnetic disk or an optical disk.

  The computer system 900 also includes an instruction input unit 903 having a keyboard, a mouse, and the like as a function unit that forms a user interface, and a display output unit 904 that presents a user with predetermined information such as a guidance screen and a processing result during operation. An image input device (scanner unit) 930 that reads an image to be processed, an image output device 950 that outputs an image processed by the image processing device to a predetermined output medium (for example, printing paper), and each functional unit And an interface unit 909 having the interface function.

  As the interface unit 909, in addition to a system bus 991 that is a transfer path of processing data (including image data) and control data, for example, a scanner IF unit 995 that functions as an interface with the image input device 930, an image output device 950, and the like. It has a printer IF unit 996 that functions as an interface with other printers, and a communication IF unit 999 that mediates transfer of communication data with the network 9 such as the Internet.

  The display output unit 904 includes a display device for presenting main information such as the read whole image and guidance information. The display device is preferably arranged in the vicinity of the instruction input unit 903 so as to efficiently perform a predetermined input operation while confirming the displayed information.

  The display output unit 904 includes, for example, a display control unit 942 and a display unit 944 made up of a CRT (Cathode Ray Tube) or LCD (Liquid Crystal Display). For example, the display control unit 942 displays guidance information, the entire image captured by the image reading unit 905, and the like on the display unit 944. Note that by using the display unit 944 having the touch panel 945 on the display surface, the instruction input unit 903 for inputting predetermined information with a fingertip or a pen can be configured.

  The computer system 900 is connected to the image input device 930 corresponding to the image acquisition unit 10 of the above-described embodiment, particularly the light receiving unit 140 to the read signal processing unit 14. This image input device 930 has the function of an image input terminal. For example, by using a full-width array of a CCD solid-state imaging device, the image input device 930 irradiates the document sent to the reading position with light, thereby displaying an image on the document. Read and convert analog video signals of red R, green G and blue B representing the read image into digital signals.

  Further, an image output device 950 is connected to the computer system 900. The image output device 950 uses, for example, an electrophotographic method, a thermal method, a thermal transfer method, an ink jet method, or a similar conventional image forming process to display an image represented by an image signal obtained by the image input device 930. Thus, a visible image is formed (printed) on plain paper or thermal paper.

  Therefore, the image output device 950 operates as an image processing unit 952 that generates print output data such as binary signals of yellow Y, magenta M, cyan C, and black K, for example, and the image processing device operates as a digital printing system. A raster output scan-based print engine 954.

  In such a configuration, the CPU 912 controls the entire system via the system bus 991. The ROM 913 stores a control program for the CPU 912 and the like. The RAM 915 is configured by SRAM (Static Random Access Memory) or the like, and stores program control variables, data for various processes, and the like. In addition, the RAM 915 stores an electronic document (not only character data but also image data) acquired by a predetermined application program, and image data acquired by an image reading unit (image input device 70) provided in the own device. In addition, an area for temporarily storing electronic data obtained from the outside is included.

  For example, a program for causing a computer to execute image processing is distributed through a recording medium such as a CD-ROM. Alternatively, this program may be stored in the FD instead of the CD-ROM. In addition, an MO drive may be provided to store the program in the MO, or the program may be stored in another recording medium such as a nonvolatile semiconductor memory card such as a flash memory. Furthermore, the program may be downloaded and acquired from another server or the like via the network 9 such as the Internet, or may be updated.

  As a recording medium for providing the program, in addition to FD and CD-ROM, an optical recording medium such as DVD, a magnetic recording medium such as MD, a magneto-optical recording medium such as PD, a tape medium, and a magnetic medium. A semiconductor memory such as a recording medium, an IC card, or a miniature card can be used. Part or all of the image processing functions of the image processing apparatus can be stored in an FD or CD-ROM as an example of a recording medium.

  Further, the hard disk device stores data for various processes by the control program, temporarily stores a large amount of image data acquired by the image reading unit (image acquisition unit 10), print data acquired from the outside, and the like. Or the area to be. The hard disk device, FD drive, or CD-ROM drive is used, for example, for registering program data for causing the CPU 912 to execute processing such as content acquisition, address acquisition, or address setting by software. .

  Note that a processing circuit 908 may be provided in which not all processing of each functional part related to image processing of the image processing apparatus is performed by software, but part of these functional parts is performed by dedicated hardware. In this case, as shown in the drawing, a correction calculation processing unit 984 corresponding to the correction calculation processing units 414 and 444 and the like, gradation correction units 986 and 987 corresponding to the gradation correction units 453 and 457, and the like may be provided individually. Good.

  Although the mechanism performed by software can flexibly cope with parallel processing and continuous processing, the processing time becomes longer as the processing becomes complicated, so that a reduction in processing speed becomes a problem. On the other hand, it is possible to construct an accelerator system with a higher speed by using a hardware processing circuit. Even if the processing is complicated, the accelerator system can prevent a reduction in processing speed and can calculate a high throughput.

1 is a side sectional view illustrating an outline of an embodiment of an image reading apparatus including an image processing apparatus including an example of an in-plane position reference type color unevenness correction unit according to the present invention. It is a figure which shows the structural example of a light-receiving part. It is the block diagram which showed 1st Embodiment of the signal processing function of an image acquisition part. It is a functional block diagram which shows the color nonuniformity correction | amendment part of 1st Embodiment. It is a figure which shows an example of the spectral sensitivity characteristic of the CCD line sensor currently used for the light-receiving part. It is a figure for demonstrating how the relationship between the density | concentration of a document and the output signal of a photodetector changes with the density | concentrations of an on-chip filter. It is a figure which shows an example of the reading value dispersion | variation (error part) by filter dispersion | variation, Comprising: It is a figure which shows what re-plotted the graph of FIG. 6 by making the relative error of each filter density | concentration into a vertical axis | shaft. It is the block diagram which showed 2nd Embodiment of the signal processing function of an image acquisition part. It is a figure which shows an example of the chart used when performing printing density nonuniformity measurement using the reading part which reduced the reading surface nonuniformity. It is the block diagram which showed 3rd Embodiment of the signal processing function of an image acquisition part. It is the block diagram which showed 4th Embodiment of the signal processing function of an image acquisition part. It is a figure explaining the process of the one function part in the color nonuniformity correction part of 4th Embodiment. It is the block diagram which showed 5th Embodiment of the signal processing function of an image acquisition part. It is a figure explaining the process of the one function part in the color nonuniformity correction part of 5th Embodiment. It is a figure which shows an example of the image (test chart) used for the color nonuniformity correction | amendment in the color nonuniformity correction part of 5th Embodiment. It is the figure which showed an example of the hardware constitutions in the case of implement | achieving an image processing apparatus by software using an electronic computer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Image reading apparatus, 10 ... Image acquisition part, 14 ... Read signal processing part, 16 ... Optical scanning system, 40 ... Image processing part, 140 ... Light receiving part, 142 ... Line sensor, 143 ... Drive circuit, 180 ... Central calculation Control unit, 250 ... shading correction circuit, 251 ... line memory, 410, 440, 450, 460, 470 ... color unevenness correction unit, 412 ... subtraction unit, 413 ... product-sum operation unit, 414, 444, 454, 464, 474 ... correction calculation processing unit, 415, 445, 455, 465, 475 ... correction coefficient storage unit, 420 ... input tone correction unit, 430, 4780 ... standardized color correction unit, 449 ... data holding unit, 453, 463, 473 ... Gradation correction unit, 457, 467, 477 ... gradation correction unit, 461, 471 ... sub-scanning direction averaging processing unit, 462, 472 ... numerical data string processing unit, 476 ... Scanning direction averaging unit

Claims (15)

An image processing method for correcting color unevenness existing in a read image,
For each color data to be processed, color data that has been corrected for color unevenness is obtained by performing gain correction for each reading position on the color to be processed and at least one other color data. An image processing method. 2. The image processing according to claim 1, wherein in the process of converting color data of a predetermined color space representing the read image into standard color coordinate data and outputting the data, the color data corrected for color unevenness is acquired. Method. 2. The image processing method according to claim 1, wherein the color unevenness corrected color data is acquired based on a result of applying gain correction to a function of a difference between two color data. The image processing method according to claim 3, further comprising acquiring the color data that has been corrected for color unevenness based on a result obtained by applying gain correction to a power of a function of a difference between data of two colors. . An image processing apparatus that corrects uneven color in a read image,
A color unevenness correction unit that obtains color unevenness corrected color data by performing gain correction for each read position for each color data to be processed and at least one other color data other than the color to be processed An image processing apparatus comprising: The image processing apparatus according to claim 5, further comprising a standardized color correction unit that converts color data of a predetermined color space representing the read image into standard color coordinate data. The image processing apparatus according to claim 6, wherein the color unevenness correction unit is arranged in front of the standardized color correction unit. The color unevenness correction unit
Arranged in the subsequent stage of the standardized color correction unit set to a plain coefficient setting,
The image processing apparatus according to claim 6, wherein the color data that has been corrected for color unevenness is converted into standard color coordinate data. The color unevenness correction unit
The image processing apparatus according to claim 5, wherein the color unevenness corrected color data is acquired based on a result of gain correction performed on a function of a difference between two color data. The color unevenness correction unit further acquires the color data that has been corrected for color unevenness based on a result of applying gain correction to a power of a function of a difference between two color data. The image processing apparatus according to 9. The image processing apparatus according to claim 5, wherein the color unevenness correction unit includes a correction coefficient storage unit that stores the gain correction coefficient for each reading position. The image processing apparatus according to claim 5, further comprising: a standardized color correction unit that converts data to be processed into standard output for color data to be processed. A light receiving unit for reading a color image;
For each color data of the processing target image acquired by the light receiving unit, color data that has been corrected for color unevenness by performing gain correction for each reading position on the processing target color and at least one other color data other than that. An image reading apparatus comprising: a color unevenness correcting unit that acquires A light receiving unit for reading a color image;
For each color data of the processing target image acquired by the light receiving unit, color data that has been corrected for color unevenness by performing gain correction for each reading position on the processing target color and at least one other color data other than that. Color unevenness correction unit to obtain
An image forming apparatus comprising: an image forming unit that forms a color image on a predetermined recording medium based on color data output from the color unevenness correcting unit. A program for performing image evaluation processing for evaluating image quality related to spatial frequency in an image using a computer,
A color unevenness correction unit that obtains color unevenness corrected color data by performing gain correction for each read position for each color data to be processed and at least one other color data other than the color to be processed A program characterized by functioning as

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